iwlwifi: mvm: disable CTS to Self

Firmware folks seem say that this flag can make trouble.
Drop it. The advantage of CTS to self is that it slightly
reduces the cost of the protection, but make the protection
less reliable.

Cc: <stable@vger.kernel.org> [3.13+]
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>